1. Field of the Invention
This invention relates to an image forming apparatus and image forming method, employing a rotary-type developing device or similar developing device.
This application claims priority from Japanese Patent Application No. 2004-331632, filed on Nov. 16, 2004, the entire contents of which are incorporated herein by reference.
2. Description of Related Art
In a rotary-type image forming apparatus, a rotary-type developing device is used in which four developers, in which are contained toner in each of the colors cyan (CY), magenta (M), yellow (Y), and black (BK), are housed integrally in a single drum, and this developing device is placed in proximity to the circumferential surface of a photosensitive drum; in addition, an endless intermediate transfer belt (transfer member) which undergoes rotating motion contacts the circumferential surface of the photosensitive drum on substantially the side opposite the developing device. By rotating the drum of the developing device by a prescribed angle each time and supplying toner in each of the colors, in order, from each of the developers onto the photosensitive drum, each of the electrostatic latent images formed for each color on the photosensitive drum is developed, in order, as a toner image in each of the colors. Each of the toner images is transferred in superposition and in order from a prescribed transfer position on the intermediate transfer belt accompanying the rotation of the photosensitive drum, and by further transferring each of the toner images onto transfer paper from the intermediate transfer belt, a color image is printed onto the transfer paper (see for example Japanese Unexamined Patent Application, First Publication No. H07-64365).
In such a conventional image forming apparatus, the motor (pulse motor or similar) used to rotate the rotary-type developing device by a prescribed angle each time may fall out of step due to load fluctuations resulting from aging or similar, so that developers may no longer be stopped at regular positions. When developers deviate substantially from normal positions, time is required for corrective rotation control. Furthermore, a prescribed image starting position is stipulated on the endless intermediate transfer belt moving in rotation at a constant speed, in order to indicate the starting position for image formation; if, during corrective rotation control, the image starting position moves past the transfer position, there is a problem in that it is necessary to wait until the intermediate transfer belt rotates one cycle and the image transfer position again reaches the transfer position, so that the printing time is lengthened.